Ozone is applied to the recirculation aquaculture system to reduce bacteria and parasites. Besides the sterilization effects, it is known that ozone has oxidizing effects on some water quality parameters. Therefore, oxidizing effects of ozone on ammonia (NH 4 -N), nitrite (NO 2 -N), nitrate (NO 3 -N), and dissolved organic carbon were tested in this study. During the test, ozone effects on pH, dissolved oxygen (DO) and bromination were also monitored. Ozone concentrations were originally set to 0.05, 0.1, 0.15, 0.2, and 0.25 ppm, but actual treatment concentrations were maintained at 0.04, 0.11, 0.15, 0.19, and 0.23 ppm. The 5 ppm of NH 4 -N was oxidized within 12 h in all concentrations of ozone treatments, with the average oxidizing rate of 0.65 ± 0.28 mg NH 4 -N/L per h. The 5 ppm of NO 2 -N was oxidized within 1.5 h in all concentrations of ozone treatments at a rate of 4.5 mg NO 2 -N/L per h. One of 5 ppm NO 3 -N was oxidized by all concentration of ozone treatment after 24 h. In addition, ozone also oxidized dissolved organic carbon and maintained the concentration at about 2.9 ± 0.77 ppm from the 15 ppm of initial concentration by 12 h. DO was increased from 5.9 to 9.4 ppm within 30 min in all ozone treatment and stabilized thereafter. Bromate concentrations increased sharply within the first 6 h of ozonation at the rate of 7.3 ± 2.4 mg/L per h in almost all ozone treatments; the rate decreased to 2.5 ± 0.15 mg/L per h thereafter. However, bromate concentration was not increased in the ammonia experiment until all ammonia was oxidized. Therefore, further studies are needed to determine the relationship between NH 4 -N concentration and bromate formation in seawater.

Caulerpa racemosa (sea grapes) and Ulva lactuca (sea lettuces) are edible green seaweeds and good sources of bioactive compounds for future foods, nutraceuticals and cosmeceutical industries. In the present study, we determined nutritional values and investigated the recovery of bioactive compounds from C. racemosa and U. lactuca using hot water extraction (HWE) and subcritical water extraction (SWE) at different extraction temperatures (110 to 230 ºC). Besides significantly higher extraction yield, SWE processes also give higher protein, sugar, total phenolic (TPC), saponin (TSC), flavonoid contents (TFC) and antioxidant activities as compared to the conventional HWE process. When SWE process was applied, the highest TPC, TSC and TFC values were obtained from U. lactuca hydrolyzed at reaction temperature 230 ºC with the value of 39.82 ± 0.32 GAE mg/g, 13.22 ± 0.33 DE mg/g and 6.5 ± 0.47 QE mg/g, respectively. In addition, it also showed the highest antioxidant activity with values of 5.45 ± 0.11 ascorbic acid equivalents (AAE) mg/g and 8.03 ± 0.06 trolox equivalents (TE) mg/g for ABTS and total antioxidant, respectively. The highest phenolic acids in U. lactuca were gallic acid and vanillic acid. Cytotoxic assays demonstrated that C. racemosa and U. lactuca hydrolysates obtained by HWE and SWE did not show any toxic effect on RAW 264.7 cells at tested concentrations after 24 h and 48 h of treatment (p < 0.05), suggesting that both hydrolysates were safe and non-toxic for application in foods, cosmeceuticals and nutraceuticals products. In addition, the results of this study demonstrated the potential of SWE for the production of high-quality seaweed hydrolysates. Collectively, this study shows the potential of under-exploited tropical green seaweed resources as potential antioxidants in nutraceutical and cosmeceutical products.

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The Socio-Ecological System (SES) perspective is widely used to identify and explain the relationship between seagrass ecosystem and their dependent community. These relationships can be recognized when humans utilize the seagrass ecosystem that benefits as a dependent community. Further, these utilization patterns can be used as a basis for managing the seagrass ecosystems themselves. This study was conducted to identify and map the relationship between seagrass ecosystem and their communities in Wangi-wangi Island, Kaledupa Island and Tomia Island. The data were collected in June–July 2019 through observation, focused group discussions and interviews with 59 respondents. The relationship between the seagrass ecosystem and its community was analyzed descriptively. The results show that the SES built a simple pattern. Seagrass ecosystems were used as the main source of daily food for island people. Seagrass products were traded limited inside the island. Resource users, infrastructure providers, as well as public infrastructure formed a short-chain. It is important to preserve the condition of seagrass ecosystems by ensuring existing legal rules and local wisdom to enhance the SES.

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